It’s a problem that’s kicking up more and more: dust control. Flying around such common areas as construction sites, unpaved roads, and mines, dust – sometimes referred to as “fugitive dust” – can create such hazards as reduced visibility, increased respiratory illnesses, and wear and tear on mechanical equipment.
Water trucks have often been used at construction sites – one of the most common source points of dust – to keep disturbed areas moist. That solution is temporary.
Construction contractors and other organizations are turning to more short-term solutions, such as applying additives or tackifiers to the soil surface. Soil stabilizers and revegetation to create durable surfaces on trails or unpaved roads are among long-term solutions.
“There are environmental problems involved with dust, safety problems, and replacement costs of building material that can all be somewhat taken care of with some kind of dust-control program,” says Craig Prete, president of Dustbusters in Evanston, WY.
One of the strictest areas in the country with respect to dust control is California. Jim Walker, who coordinates operations for the Bob Hope Chrysler Classic golf tournament in Rancho Mirage, CA, points out that California mandates that any overturned ground must be stabilized.
Walker’s company stabilizes parking areas with a polymer product, Envirotac II from Environmental Products and Applications, before and after tournaments at four venues, treating areas up to 40 ac. “It seems like the most feasible costwise, and it does the job,” Walker says. “It’s an instant shot, and there’s really no other maintenance with it.”
For environmental safety, Walker prefers the polymer to a salt solution the company used years ago, which went directly into the storm system after a rain event. “But this one, with its gluing effect, doesn’t seem to run off,” he says.
Wind, especially in desert areas, is a concern for Walker, as it is for Prete, who says coal mines are among his company’s most challenging jobs. Strip-mining operations generate a lot of fugitive dust and, in windy conditions, can reduce visibility, destroy or retard vegetation, and require increased equipment maintenance. The mines are under strict regulations regarding the control and containment of dust, he adds.
Prete says he uses magnesium chloride because it’s prevalent in his area and its cost-benefit ratio is better than anything else in his region, including emulsions and polymers.
“Because of the new attention being given to dust-control problems, we’ve seen a real increase in the amount of product sold and actually in the number of applications,” he says, noting that this is especially true at Powder River Basin in northeastern Wyoming. “At the same time, we think it benefits the mines by saving them money [compared to] other methods of controlling the dust, such as watering. Hopefully it’s a win/win situation where there’s less dust and at the same time a better environment and less cost for the mine.”
Dustbusters began treating mines in 1980. Most of the mines have set up a program of using magnesium chloride, such as DustGard from North American Salt, Prete notes.
“It’s the best-cost option for them in this area,” he says. “I don’t know that it’s the best option in all areas, but it is in this area because the cost of the product is relatively inexpensive and it’s the best solution to the problem.”
Near the copper mines of Salt Lake City, UT, Jerry Shepherd’s company, Kennicott Utah Copper, has recently been involved in revegetating three-fifths of a 10,000-ac. impoundment near a copper mine. “In the tailings, it doesn’t grow really well, so we use a lot of biosolids from Salt Lake City,” says Shepherd, the company’s contract coordinator. “Not everything we do we can get biosolids on, because there’s not enough.”
Shepherd’s company also uses a mixture of wheat and rye grasses, “and that’s the best dust control,” he says. “If you can get that to grow, you’ve got your dust control.”
Fresh sand is used on active cells, and in dormant areas the company uses 60 high-pressure sprinklers that shoot water within 600 ft., at 1,000 gal./min. In other areas, seed is used as well as polymer. “That’s usually good for a year, but if it gets torn up or sand starts getting blown over on it, then we use additional polymer. On the roads we also use magnesium chloride,” Shepherd says.
Greg Babington, construction manager for Canyons at Big Horn in Palm Desert, CA, a golf and lot sales developer, uses Soil-Sement, a polymer emulsion, for dust control in both short-term and long-term situations, for both small and large projects.
“It’s the best product I’ve found that is flexible in ratio mixtures to use for many things other than just dust control,” says Babington, who adds that he’s used it on many surfaces, from travel surfaces to parking facilities.
In considering such areas as roads, companies must often choose between paving and a stabilization method. Cost is usually the deciding factor. Says Babington, “The cost of applying Soil-Sement at a ratio conducive to roadway is far less than any paving alternative out there. When blended with certain aggregate materials, it makes a very fine road once it’s cured.”
Prete agrees that the biggest difference is in cost but believes that if vegetation is possible, it’s preferred. “But there are areas where revegetation is not going to happen, and in those cases, obviously suppression is preferred to just letting the dust fly,” he says.
“If you have a road that has only a limited number of vehicles per day and you can’t justify the cost of paving, then alternate solutions are to do some sort of dust-control program,” he adds. The amount of treatment done on an unpaved road also will determine how much traffic the road can handle, Prete notes.
Lou Snow, vice president of Dust Pro in Phoenix, AZ, a company that provides erosion control and dust-control services, has a slightly different take, while concurring that cost is the primary factor. “You have to address cost compared to whatever you’re going to be looking at, and that would be either to do nothing and accept your regulatory fines or to have it paved or sealed or whatever, so topical dust suppressant is the least expensive, even compared to water,” Snow says.
“Even if someone at a construction site is running a water truck, the topical dust suppressants are typically less expensive on a project because you’re using less water and you’re not running vehicles as much,” he adds.
Babington points out that comparing the cost of revegetation of a site with the cost of long-term soil stabilization isn’t really fair. “Soil-Sement can be used in slope revegetation projects to temporarily hold the grade in place until the landscape material takes root, but you can’t really compare vegetation and Soil-Sement. The vegetation has a purpose aesthetically, as well as from a soil erosion standpoint, whereas the Soil-Sement itself has no aesthetic value,” he says.
Even though biosolids are free, revegetation of mining areas is costly, Shepherd points out. “The cost is unfailingly excessive because you’ve got no nutrients in the soil, and so it’s all ready to blow if you don’t do anything. We have to do extra; we just don’t drill. We even use polymer on top of what we seed because sometimes when we seed, if we don’t get enough rain in the meantime to hold the dust down while the seed’s taking, we lose all the seed.” He recounts the time a few years ago when his company lost seed on 600 ac. under those conditions.
These days, companies have a wide range of products from which to choose, including organic and inorganic chemical products. Inorganic materials are usually produced as a side stream from another manufacturing process and include polymers and different emulsions. Organic materials include materials harvested from trees, resins, lignins, chlorides that come from the salt in water bodies, and natural enzymes. Organic products are less expensive than inorganic and generally perform as well, Snow says.
Snow advises that those buying dust-control chemicals check out the track records of the products. “One product will not solve all the problems we have in this country for dust control, so [the buyer] has to be aware of the products and how they perform.”
Application methods vary. For the sub-base, one must strengthen the soil, Snow explains. “If you’re talking about a wearing course, for example, some of these materials you have out there that you can use for base are actually ingredients you mix into the subgrade, whatever depth that you’re dealing with – say 3 or 4 inches – and that becomes the lift, the wearing course itself.” In many cases, users put something on the surface, such as chip seal, slurry seal, or asphalt, he notes. “But you are actually strengthening your subgrade, so you’re increasing the longevity of the wearing course,” Snow says. “That in itself is a lot less expensive than applying an asphalt or a chip seal on a dirt surface without stabilizing that surface. You’re going to have a shorter life [without stabilization] because you’re going to have cracks and degradation.”
How Long Will It Last?
Correct application of the product is also essential, Snow points out. “For example, in application you have one end user putting down material with a water truck versus another end user putting it down with a conventional applicator. Typically the controlled applicator will last. Longevity of the product will increase tremendously because they controlled the application rate. They’re just not throwing it all over the surface.”
Prete says his company applies magnesium chloride to the surface and allows it to soak in and filter through. “Magnesium chloride needs to be near the surface because it is a hygroscopic product, which means it draws moisture from the air,” he explains. The chemical is sprayed in liquid form onto the surface with a spreader truck or other spray equipment. Prete says the product has to be reapplied about once a year on county roads and about two to four times a year on heavily traveled roads near mines.
Dustbusters typically applies the product two to four times a year “because with 150- and 200-ton haul trucks running on the road, it obviously won’t last as long as with a car or pickup,” Prete says. “Usually there’s a little bit of a lighter application, but it is treated more frequently.” At the mines, it is applied before prewatering and then it is spread on the surface, Prete says.
Although Soil-Sement can be applied a number of ways, one of the most common is to use a truck equipped with a tank and a pump, users note. “It can be applied on the surface via a hose or a spray bar apparatus,” Babington says. “Surface application is one way to do it. Another way is to blend it in with the soil, which actually gives you a much better surface crust and holds it for a much longer time. I’ve used it in very light concentrations of surface application to extremely heavy applications, blended 8 to 10 inches deep into the soil. Its versatility is almost endless.”
Light applications are not well suited for traffic use, Babington says. “A light application might only be usable for pedestrian foot traffic, where the need for long-term dust holding power might require a heavier ratio to penetrate a little bit deeper into the soil and at the same time might not be good for vehicular traffic. Until you start blending the product into whatever materials your site has to offer, which differ very much from site to site, it depends on how much material and what ratio of blending you might use to achieve the result you’re trying to get,” he says.
For application of dust-control products, one must do a complete area “or you’re wasting your time, because one area will blow over on top of another area,” Shepherd says.
But once grass grows, a new application doesn’t have to be done for a long time, he states. In new areas, reapplication is required at least in the following year, he adds. “In our active areas, we’re having to reapply polymers every couple months.”
As for roads, Snow says it’s not possible to know precisely how much traffic an unpaved road treated with stabilization products can handle. “[It] depends on the ratio of the product to gallons of water and some preparation of the existing ground,” says Babington.
“There are too many variables,” says Snow. “One, you have to address the soil type because you can have a clay soil or sandy soil; different soils take different types of treatments. Two is the frequency and type of traffic: Are you going to be running Sherman tanks or a little old lady on her bicycle? You’ve got different traffic considerations because of that. Three is Mother Nature. Do you have proper drainage on the surface? Is this a sideslope area? You have to address all of that before you determine how long the material is going to last, and each one of those has its own effect.”
And whether on a road or at a mine, a variety of factors affects dust-control longevity, including rainfall and humidity. “We’ve had topical applications last up to two years on a single application and we’ve had it last as little as two months,” Snow says. “We’ve had sub-base applications, and we’ve got some of it lasting four to five years.”
Humidity is good for magnesium chloride, Prete notes. “It allows the magnesium chloride to regenerate and keeps the product active. Light rain also is helpful, but a really heavy rain in a short period of time can cause some of the magnesium chloride to leach out.”
Rainfall does not affect the application of polymer, Shepherd says. “It softens up and then it’ll harden up again after the rain. It’s not a problem because it’s like paint: It cures at only 50Âº [Fahrenheit]. If you’re down to freezing temperatures, it’s worthless to you.”
Wind is the primary factor, Shepherd notes. “If you want it to hold down in 60-mile-per-hour winds, you’ve got to have a quarter-inch of crust of polymer, which is about 300 gallons an acre. If you only want an eighth of an inch and you’re only looking at 35-mile-per-hour winds, then it’s only 150 to 200 gallons an acre.”
The polymer is like glue that dries clear and forms a crust, Shepherd says. In his company’s case, it is binding sand particles; in other cases, it might be soil particles.
Product users must ensure that whatever products they use meet environmental criteria and are not carried off with stormwater, Snow points out. Most products are stable, especially when mixed into the soil, he adds.
“If you’re just shooting something on the surface, then you’ve got to be concerned if it’s water emulsible and, if it is, how it’s going to affect the environment, especially with Phase II and stormwater runoff,” he says.
Shepherd says the polymer is fairly stable during rain events. “With the polymer, you go out after it rains and you can hardly tell that it’s there, but as soon as it dries, it hardens right back up. After a rain cycle of a year, there’s still a crust but not the crust that you once had. It actually works for more than a year, but a year is a pretty good span.”
As for the magnesium chloride’s environmental implications – whether it is carried off from treated surfaces by stormwater – Prete says studies show that in the testing of the chemical, it does not migrate very far from the road surface before it breaks down into the natural elements of magnesium and chlorides.
“Probably one of the biggest users out here in the West is the [United States] Forest Service,” Prete notes. “They’ve done considerable testing on their own to make sure that they’re not damaging the environment. It’s nonhazardous and seems to be pretty compatible with the environment.”
Babington also says the environmental implications of Soil-Sement are nil. “The [material safety] data sheets and environmental impact reports written on the product when it was originally devised indicate none,” he says.
The South Coast Air Quality Management District in California, formed to control airborne pollutants, including dust, has dictated by some studies that particulate matter 10 microns in diameter and smaller (PM10) would be the level at which dust suppression should be achieved, Babington says. “Once the product is used, the PM10 material sizes are held down.”
Snow states that he would like to see uniform standards in dust control. “That’s something we’re lacking that I’ve been trying to push here for the last few years: to establish some standards within the industry that everybody could understand and adhere to. That’s something that’s been difficult – to get competitors together to establish standards and have everybody agree on the same thing. Everybody could share and benefit from this and see what products perform the best under what conditions. It all relates to cost as well.”